Microchannel plate and process for producing the same

ABSTRACT

A method of manufacturing microchannel plate according to an embodiment of the present invention includes: a first step of fabricating a multifiber having a polygonal cross-section by bundling a plurality of fibers; a second step of fabricating a microchannel plate base material by use of a plurality of the multifibers; and a third step of fabricating a microchannel plate out of the microchannel plate base material. The plurality of fibers include: a first fiber whose predetermined-thickness outer circumferential part surrounding a center part including a core is formed of a predetermined-component glass material; and a second fiber whose both center part including a core and outer circumferential part surrounding the same are formed of the predetermined-component glass material. The second fiber is arranged at, at least, one corner of a polygonal cross-section of the multifiber.

TECHNICAL FIELD

The present invention relates to a microchannel plate used for aphotomultiplier tube or the like and a manufacturing method thereof.

BACKGROUND ART

A microchannel plate has a plate-like structure and has a regularlyarrayed structure of a plurality of channels. In recent years, due toexpansion in the field of use, widening in the open area ratio andminiaturization of the channels have been required for microchannelplates. With the widening in the open area ratio and miniaturization,due to a misalignment (see FIG. 6) of hexagonal multifibers with eachother at the time of manufacturing, a failure of a ring-like connectionof channels with each other (a so-called missing wall phenomenon) and abreakage failure of channel walls (a so-called Rosetta phenomenon)easily occur at corners of multifibers adjacent with each other.

As conventional art for solving the above-described problems, disclosedin the specification of U.S. Pat. No. 4,431,694 Patent Document 1 is amethod for preparing, when aligning a large number of standard fibers tofabricate a multifiber, a small number of special fibers having thickercladding glass tube walls than those of the standard fibers andarranging these at corners of the hexagonal multifibers.

DISCLOSURE OF THE INVENTION

However, with this method, when miniaturization of channels is intended,the probability of occurrence of the missing wall phenomenon and Rosettaphenomenon increases during a process of fusion-bonding of the fibers toeach other by heating and pressurization. Therefore, it is difficult tomanufacture microchannel plates at a high yield. Moreover, with thestructure described in Patent Document 1, a microchannel plate havinghigh accuracy and high density cannot be realized.

An object of the present invention is to provide a method ofmanufacturing microchannel plate for which such problems have beensolved and a microchannel plate allowing arraying of minute channels athigh accuracy and high density.

A method of manufacturing microchannel plate according to the presentinvention includes: a first step of fabricating a multifiber having apolygonal cross-section by bundling a plurality of fibers and reducingthe same in diameter; a second step of fabricating a microchannel platebase material by use of a plurality of the multifibers; and a third stepof fabricating a microchannel plate by slicing the microchannel platebase material into flat plates, wherein the plurality of fibers bundledin the first step includes: a first fiber whose predetermined-thicknessouter circumferential part surrounding a center part including a core isformed of a predetermined-component glass material; and a second fiberwhose both center part including a core and outer circumferential partsurrounding the same are formed of the predetermined-component glassmaterial, and the second fiber is arranged at, at least, one corner of apolygonal cross-section of the multifiber.

According to this invention, a multifiber having a polygonalcross-section is constructed by bundling a first fiber whose outercircumferential part is formed of a predetermined-component glassmaterial and a second fiber whose both center part and outercircumferential part are formed of the predetermined-component glassmaterial, and the second fiber is arranged at, at least, one corner ofthe polygonal cross-section, so that a channel itself is not formed atthis corner. Therefore, the second fiber acts as a dummy to increase theamount of the predetermined-component glass material at the corner,provides an effect of the corner to thicken a channel wall by the firstfiber, and thus can reduce the probability of occurrence of a failuresuch as a missing wall phenomenon and a Rosetta phenomenon. And,although a reduction in the number of channels at the corner due toarrangement of the second fiber at the corner of the polygonalcross-section brings about a slight decline in luminance, this isnegligible from a practical point of view when taking into considerationthe fact that a problem of bright spots, an image defect, and the likedue to a missing wall phenomenon and a Rosetta phenomenon can be solved.

In the method of manufacturing microchannel plate according to thepresent invention, it may be possible that the predetermined-componentglass material has an insolubility in response to apredetermined-component solvent, the center part of the first fiber isformed of a glass material having solubility in response to thepredetermined-component solvent, and the third step includes a step ofexposing a sliced flat plate to the predetermined-component solvent.

In this manner, the thickness of the center part of the first fiber tobe a channel becomes equivalent across the entire flat plate, so thatthe soluble glass material that forms the center part is uniformlyremoved at a high yield by exposing the flat plate to apredetermined-component solvent. Therefore, in comparison with themethod of Patent Document 1 wherein a soluble glass material thinlyremains at the corner of a multifiber, it becomes possible to fabricatea further miniaturized microchannel plate.

Moreover, in the method of manufacturing microchannel plate accordingthe present invention, it is preferable that the first step is a step offabricating a multifiber having a hexagonal cross-section. In thismanner, channels of a microchannel plate can be most closely aligned, sothat the channels occupy a large area, and the microchannel plate can beimproved in sensitivity.

Furthermore, in the first step of the method of manufacturingmicrochannel plate according to the present invention, it is preferablethat the second fiber is arranged at adjacent two corners, two cornersexcluding a neighbor, two corners located symmetrically, four cornersexcluding corners located symmetrically, four corners excluding adjacentcorners, or all corners of the hexagonal cross-section of themultifiber. In this manner, after a plurality of multifibers arealigned, the number of second fibers in a corner region between adjacentmultifibers is uniformized, so that the probability of occurrence of afailure is uniformly reduced in all corner regions.

A microchannel plate according to the present invention is amicrochannel plate including: a glass effective portion for which aplurality of channels are formed; and a glass rim portion surroundingthe effective portion, the microchannel plate being shaped in aflat-plate form, wherein the effective portion is constructed byarranging multifiber portions each formed by bundling a plurality ofchannels in a polygonal shape, without a gap so that corners thereof areadjacent to each other, and the number of channels per unit area in acorner region where the corners are adjacent to each other is smallerthan the number of channels per unit area in a peripheral region of thecorner region. The effective portion has a plurality of multifiberportions each formed by bundling a plurality of channels in a polygonalshape so as to have a plurality of corners, each of the plurality ofmultifiber portions being arrayed so as to form a corner region where acorner thereof and a corner of another adjacent multifiber portion ofthe plurality of multifiber portions are adjacent to each other. Anumber of the channels per unit area in the corner region is smallerthan a number of the channels per unit area in a peripheral region ofthe corner region.

According to the present invention, since the number of channels perunit area in the corner region is smaller than the number of channelsper unit area in the peripheral region of the corner region, the channelwalls are relatively thickened. Therefore, failures such that thechannels are connected to each other are reduced in the corner region,so that this rarely causes a failure of bright spots, an image defect,and the like. Moreover, a decline in luminance of the corner area due tothe relatively thickened channel walls does not have a great influenceon the image quality as a whole in use of the microchannel plate.

In the microchannel plate according to the present invention, it isdesirable that an inside diameter of the channels in the corner regionis equivalent to an inside diameter of the channels in the peripheralregion of the corner region. With such a microchannel plate, since thechannel inside diameter is equivalent between the channels in the cornerregion and the channels in the peripheral region thereof, theconcentration of residual gas accumulated in the channel is comparablebetween the corner region and the peripheral region thereof when usingthe microchannel plate as a vacuum tube component or the like.Therefore, no problem that occurrence of bright spots or the like due toan electrical discharge, ion feedback, or the like is concentrated inthe corner region occurs. Moreover, gas venting before the microchannelplate is used as a vacuum tube component or the like is also carried outequally to the respective channels. Therefore, since there is no suchfailure that production of residual gas particularly increases inchannels of the corner region, occurrence of bright spots or the like inthe corner region due to an electrical discharge, ion feedback, or thelike is rare.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a part of a structure of an MCPaccording to an embodiment.

FIG. 2 are views of the MCP of FIG. 1 observed from the front.

FIG. 3 is a process drawing showing a manufacturing method of the MCPaccording to the embodiment.

FIG. 4 is a plan view showing an arrangement of fibers in an MFformation.

FIG. 5 is plan views showing other examples of a dummy fiber arrangementand an MF alignment pattern.

FIG. 6 is a plan view showing a misaligned condition of regularhexagonal MFs with each other.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Here,in the description of the drawings, identical or equivalent elements aredesignated with identical numerical symbols so as to avoid overlappingdescriptions. Moreover, in the description of embodiments, amicrochannel plate is referred to as an “MCP,” and a multifiber, as an“MF”, abbreviated, respectively.

First, a structure of an MCP according to the present embodiment will bedescribed with use of FIG. 1 to FIG. 2. Here, a case of use of an MCP 1having a circular cross-section is raised as an example.

FIG. 1 is a perspective view showing a structure of an MCP according tothe present embodiment, wherein the MCP is schematically drawn with apart broken away. The MCP 1 is shaped in a disk-like form, and iscomprised of a glass effective portion 2 having an electron multiplyingfunction and a glass rim portion 4 surrounding the effective portion 2.In the effective portion 2, a plurality of channels 6 aretwo-dimensionally regularly arrayed. These channels 6 are holes havingthe same diameter and pass through in a plate thickness direction.

FIG. 2 shows a construction of the MCP 1 of FIG. 1 observed from thefront. In FIG. 2( a), shown is a front view of the MCP 1 which isconstructed by aligning, closely in a honeycomb shape, MFs 10 eachformed by bundling a plurality of channels 6 in a hexagonal shape, andin FIG. 2( b), shown is an enlarged view of a region A in FIG. 2( a). Asshown in FIG. 2( b), in a corner region where corners of three MFs 10are adjacent to each other, since no channel exists at the corner of oneof the three MFs 10, the number of channels 6 per unit area of thecorner region is smaller than the number of channels 6 per unit area ina peripheral region of the corner region. Therefore, a failure of aring-like connection of the channels 6 in the corner region or breakageof channel walls is unlikely to occur. In this case, for the reason thatthe number of channels 6 per unit area of the corner region is smallerthan that in the periphery, luminance in the corner region can possiblydecline in use. However, in terms of the MCP 1 as a whole, the problemof a decline in luminance is almost negligible in comparison with aproblem of bright spots, an image defect, and the like due to a missingwall phenomenon and a Rosetta phenomenon.

Moreover, as shown in FIG. 2( b), the inside diameter of the channels 6located in the corner region is equivalent to the inside diameter of thechannels 6 located in the peripheral region of the corner region.Therefore, even if residual gas is discharged from the channel wall intothe channel when using the MCP as a vacuum tube component or the like,the concentration of residual gas accumulated in the channel iscomparable between the corner region and the peripheral region thereof,so that a problem that occurrence of bright spots or the like due to anelectrical discharge, ion feedback, or the like is concentrated in thecorner region does not occur. Moreover, gas venting at the final stageof a manufacturing process of the MCP before this is used as a vacuumtube component or the like is also carried out to an equal extenttherebetween since the respective channels in the corner region and theperipheral region thereof are equivalent in inside diameter. Therefore,there is no failure that occurs in the MCP disclosed in thespecification of U.S. Pat. No. 4,431,694, such that production ofresidual gas particularly increases in channels of the corner region, sothat occurrence of bright spots or the like in the corner region due toan electrical discharge, ion feedback, or the like is rare.

Next, based on FIG. 3, a manufacturing method of the MCP 1 according tothe present embodiment will be described. Here, a case of use of the MCP1 having a circular cross-section, the MFs 10 each having a regularhexagonal cross-section, and an acid solvent (for example, HNO₃ or HCl)is raised as an example.

First, a manufacturing method of the MF 10 will be described. In FIG. 3(a), shown is a forming method of a channel fiber (first fiber) 12 forwhich the channel 6 is produced by a coring process. According to FIG.3( a), the channel fiber 12 is obtained by inserting a core portion(center part) 14 formed of a first glass material having solubility inresponse to an acid into a clad portion (outer circumferential part) 16formed of a second glass material having insolubility in response to theidentical acid and then tube drawing while heating these. A dummy fiber(second fiber) 18 (unillustrated) is a column-shaped fiber obtained byusing only the second glass material having insolubility and then,similar to the channel fiber 12, tube drawing while heating the same.The dummy fiber 18 is made of the glass material(predetermined-component glass material) insoluble to an acid at bothits center part including the core and its predetermined-thickness outercircumferential part surrounding the same, however, as long as neitherthe center part nor the outer circumferential part is dissolved by anidentical solvent, these may be made of different types of glassmaterials comprised of different constituent elements. Also, at the timeof tube drawing, this is carried out so that the channel fiber 12 andthe dummy fiber 18 become circular in cross-section.

Next, in a form 20 having a regular hexagonal hollow cross-section asshown in FIG. 3( b), the channel fibers 12 and the dummy fibers 18 arestacked up closely in parallel in a predetermined pattern, foralignment. When aligning these, as shown in FIG. 4, the dummy fibers 18are arranged one each, of the inner walls of the form 20, at two cornerslocated symmetrically, and the channel fibers 12 are arranged throughoutthe other part. Thereafter, the channel fibers 12 and dummy fibers 18aligned in the frame 20 are fusion-bonded by heating and cooled, andthen the frame 20 is removed, thus an MF base material 22 having aregular hexagonal cross-section is obtained. Next, while heating the MFbase material 22 as shown in FIG. 3( c), tube drawing is again carriedout to form the MF 10. At this time, the tube drawing is carried out sothat a cross-section of the MF 10 becomes regular hexagonal. Here,furthermore, MFs obtained in this process that have been stacked up in aform, aligned, and tube drawn may be provided as the MF 10.Alternatively, this process may be repeated until a desired channeldiameter is obtained.

Next, a fabrication method of the MCP 1 using a plurality of MFs 10 willbe described.

First, as shown in FIG. 3( d), a plurality of the obtained MFs 10 arealigned inside a glass tube 24. At this tine, in terms of all MFs 10,the MFs 10 are closely aligned so that symmetrical lines each connectingtwo corners having the dummy fibers 18 are parallel with each other asshown in FIG. 5( a). In this manner, one dummy fiber 18 is arranged inevery corner region, and the channel fibers 12 are arranged throughoutthe peripheral region thereof, so that an increase in the area of aninsensitive part of the MCP 1 can be suppressed to a minimum.

Next, by fusion-bonding by heating while pressurizing the plurality ofMFs 10 aligned inside the glass tube 24, an MCP base material 26 isobtained (see FIG. 3( e)). Thereafter, by slicing the MCP base material26 at a predetermined thickness and a predetermined angle and applyingthereto a surface polishing as shown in FIGS. 3( f) and (g), an MCPplate material 28 is obtained.

Next, as shown in FIG. 3( h), the MCP plate material 28 is dipped in anacid solution, so as to carry out a coring process. At this time, thecore portion 14 of the channel fiber 12 is eluted since this has beenformed of the first glass material having solubility in response to anacid. On the other hand, the clad portion 16 and the dummy fiber 18 arenot eluted since these are formed of the first glass material havingsolubility in response to the acid. Therefore, the channel 6 is formedas a result of elution of the core portion 14. Here, since the diameterof the core portion 14 is equivalent between the corner region and theperipheral region thereof, the present invention is superior to the artdisclosed in the specification of U.S. Pat. No. 4,431,694 in a pointthat the first glass material is equivalently eluted, so that aso-called “uneven elution” does not occur.

Next, the MCP plate material 28 applied with a coring process is placedin an electric furnace with a hydrogen atmosphere and heated so as tocarry out a reduction process (see FIG. 3( i)). Thereby, PbO on thesurface of the channels 6 of the MCP plate material 28 is reduced to Pb,so that a desired conductive thin film is formed. At this time as well,since the channel inside diameter of the channels is equivalent betweenthe corner region and peripheral region thereof, a homogeneousconductive thin film is formed. Lastly, on both surfaces of the MCPplate material 28, a metal for an electrode is evaporated(unillustrated), thus the MCP 1 is obtained.

According to the present embodiment, when aligning and fusion-bondingthe MFs 10, even when the MFs 10 are misaligned with each other, sincethe dummy fibers 18 have been arranged one each at two corners locatedsymmetrically of the corners of a regular hexagonal cross-section of theMF 10, no such a condition that the channels 6 are connected to eachother in a ring-like form occurs, thus it becomes possible to preventoccurrence of a missing wall phenomenon or a Rosetta phenomenon.Moreover, since only one dummy fiber 18 has been arranged in the cornerregion comprised of three adjacent corners, reduction in the number ofchannels 6 is minimized, whereby an adverse effect on an image and thelike resulting from an increase in the area of the insensitive part ofthe MCP 1 can be suppressed to a minimum. Furthermore, since thechannels 6 in the corner region are the same in the hole diameter as thechannels 6 in the peripheral region of the corner region, production ofresidual gas never occurs in the channels 6 at the time of gas venting,so that occurrence of poor characteristics such as bright spots, anelectrical discharge, and ion feedback can be prevented.

Moreover, with regard to a dummy fiber arrangement in MFs and an MFalignment pattern, patterns as shown in FIG. 5( b) to (f) can bementioned. MCPs 1 fabricated in these patterns by the same manufacturingmethod as in the above-described embodiment provide the same effects asthose in the above-described embodiment (FIG. 5( a)).

In the following, dummy fiber arrangements and MF alignment in thepatterns shown in FIG. 5( b) to (f) will be described. However,description of the manufacturing method will be omitted since this isidentical to that in the above-described embodiment.

As shown in FIG. 5( b), such a construction may be employed that dummyfibers 118 are arranged one each at any two adjacent corners of the sixcorners in an MF 110 having a regular hexagonal cross-section, and nodummy fibers 118 are arranged at the other four corners. When aligningthe MFs 110, as shown in FIG. 5( b), all MFs 110 are aligned so thatsymmetrical lines each connecting two corners arranged with no dummyfibers 118 are parallel with each other and, in terms of thesesymmetrical lines, the sides having the dummy fibers 118 are arranged inthe same direction. In this manner, one dummy fiber 118 is arranged inevery corner region, and channel fibers are arranged throughout theperipheral region thereof.

As shown in FIG. 5( c), such a construction may be employed that dummyfibers 218 are arranged one each at two corners excluding a neighbor ofthe six corners in an MF 210 having a regular hexagonal cross-section,and no dummy fibers 218 are arranged at the other corners. That is, sucha construction may be employed that dummy fibers 218 are arranged at twocorners arranged in order with one corner therebetween of the sixcorners in an MF 210 having a regular hexagonal cross-section, and nodummy fibers are arranged at the other four corners.

When aligning the MFs 210, as shown in FIG. 5( c), the MFs 210 locatedin a layer S1 are aligned so that symmetrical lines each connecting twocorners having no dummy fibers 218 are parallel with each other and thesides having the dummy fibers 218 are arranged on the same side. The MFs210 located in a layer S2 are rotated by 180 degrees from the MFs 210located in the layer S1 for alignment. The layer S1 and the layer S2 arestacked up alternately. That is, as shown in FIG. 5( c), a plurality ofMFs 210 are aligned so as to form a honeycomb shape for which the row S1and the row S2 are alternately provided. The MFs 210 contained in therow S1 are arranged so that the sides having the dummy fibers 218 areoriented in the same direction, and the MFs 210 contained in the row S2are arranged so that the sides having the dummy fibers 218 are invertedby 180 degrees relative to the row S1. In this manner, one dummy fiber218 is arranged in every adjacent corner region, and channel fibers arearranged throughout the peripheral region thereof.

As shown in FIG. 5( d), such a construction may be employed that dummyfibers 318 are arranged one each at four corners excluding twosymmetrical corners of the six corners in an MF 310 having a regularhexagonal cross-section. When aligning the MFs 310, as shown in FIG. 5(d), all MFs 310 are aligned so that symmetrical lines each connectingtwo corners arranged with no dummy fibers 318 are parallel with eachother. In this manner, two dummy fibers 318 are arranged in everyadjacent corner region, and channel fibers are arranged throughout theperipheral region thereof.

As shown in FIG. 5( e), such a construction may be employed that dummyfibers 418 are arranged one each at four corners excluding adjacent twocorners of the six corners in an MF 410 having a regular hexagonalcross-section. When aligning the MFs 410, as shown in FIG. 5( e), allMFs 410 are aligned so that symmetrical lines each connecting twocorners arranged with the dummy fibers 418 are parallel with each other.In this manner, two dummy fibers 418 are arranged in every adjacentcorner region, and channel fibers are arranged throughout the peripheralregion thereof.

As shown in FIG. 5( f), such a construction may be employed that dummyfibers 518 are arranged one each at all six corners in an MF 510 havinga regular hexagonal cross-section. When aligning the MFs 510, those areclosely piled up for alignment as shown in FIG. 5( f). In this manner,three dummy fibers 518 are arranged in every adjacent corner region, andchannel fibers are arranged throughout the peripheral region thereof.

However, the present invention is not limited to the above-describedembodiment. For example, in the present embodiment, although thecross-section of the MCP 1 has been provided in a circular form, thismay be quadrangular or the like. In the present embodiment, although theacid solvent has been used, the solvent is not limited to this. Asolvent other than acid may be used as long as the solvent dissolves thefirst glass material and does not dissolve the second glass material.

Moreover, in the above-described embodiment, although the frame 20having a regular hexagonal hollow cross-section has been used whenaligning the MFs 10, one having a hollow cross-section in a hexagonalshape whose two opposed sides are long, a triangular shape, or aquadrangular shape may be used. A regular hexagonal shape isparticularly preferable in terms of arraying MFs minutely and closely.

Moreover, it is not always necessary that the dummy fiber arrangementand MF alignment are in the patterns as shown in FIG. 5( a) to (f). Itis preferable that one, two, or three dummy fibers are arranged in thecorner region.

Industrial Applicability

According to the present invention, a microchannel plate capable ofpreventing the occurrence of a missing wall phenomenon and a Rosettaphenomenon and a manufacturing method thereof can be provided.

The invention claimed is:
 1. A method of manufacturing a microchannelplate, the method comprising: (1) a first step of fabricating aplurality of multifibers each having a polygonal cross-section withthree or more corners, by bundling a plurality of fibers and thinningthe bundle, the plurality of fibers to be bundled including: a pluralityof first fibers each comprising a center part which includes a core andis formed of a first glass material with solubility to a predeterminedsolvent, and an outer circumferential part which surrounds the centerpart of the first fiber and is formed of a second glass material withinsolubility to the predetermined solvent; and a plurality of secondfibers each consisting of a third glass material with insolubility tothe predetermined solvent, the first and second fibers being bundledsuch that each of the second fibers is positioned at one or moreassociated corners of the polygonal cross-section of each of themultifibers to be fabricated; (2) a second step of fabricating amicrochannel plate base material, by arranging the plurality ofmultifibers while side portions of the adjacent multifibers, eachcorresponding to one side of the polygonal cross-section, are in contactwith each other; and (3) a third step of fabricating a microchannelplate, by slicing the microchannel plate base material into flat plates,the third step including a step of etching a slice fiat plate with thepredetermined solvent.
 2. The method of manufacturing a microchannelplate according to claim 1, wherein each of the multifibers fabricatedin the first step has a hexagonal cross-section.
 3. The method ofmanufacturing a microchannel plate according to claim 2, wherein in thefirst step, two or more second fibers are respectively arranged atadjacent two corners, two corners excluding a neighbor, two cornerslocated symmetrically, four corners excluding corners locatedsymmetrically, four corners excluding adjacent corners, or all cornersof the hexagonal cross-section of each of the multifibers fabricated. 4.The method of manufacturing a microchannel plate according to claim 1,wherein each of the second fibers comprises a center part including acore and being made of the third material, and an outer circumferentialpart surrounding the center part and being made of the third material.5. The method of manufacturing a microchannel plate according to claim1, wherein both parts of each of the second fibers, respectivelycorresponding to the center part and the outer circumferential part ofeach of the first fiber, are made of the third material.
 6. The methodof manufacturing a microchannel plate according to claim 1, wherein thesecond material and the third material are the same material.
 7. Themethod of manufacturing a microchannel pate according to claim 1,wherein the second material and the third material are differentmaterials.